The present invention relates generally to peristaltic type pumps and more particularly to a peristaltic pump having movable reaction members.
Peristaltic pumps employing a rotor having one or more compression surfaces thereon operative to effective peristaltic action on a compressible flow tube maintained in predetermined relation to the rotor are generally known. Peristaltic pumps have been developed which permit quick loading or adjustment of a compressible flow tube relative to an associated pump rotor so that little down time is required when replacing or adjusting the flow tube in a pump. Examples of such pumps are disclosed in U.S. Pat. Nos. 4,179,249 and 4,231,725, both of which are assigned to the assignee of this application and which are incorporated herein by reference. In these pumps, reaction surfaces are provided on movable reaction members, often called clam shells, which are pivotal between an open position enabling loading and removal of a tube and a closed position wherein the tube is maintained in a predetermined position to enable peristaltic pumping action to take place.
To effect efficient pumping, it is desirable that relatively large compression forces be exerted on the tube by the compression surfaces on the rotor. In some known peristaltic pumps, pump efficiency has been decreased due to the force on the reaction members opening a small gap between the respective reaction surfaces.
The reaction members shown in U.S. Pat. No. 4,231,725 are held together in the closed pumping position by an outwardly facing lock nut which is threaded onto a stub shaft to bring a frustoconical cam surface thereon into camming engagement with cam surfaces on the reaction members. In order for the nut cam surfaces to properly engage the cam surfaces on the reaction members, the reaction members must be closely adjacent the closed position, e.g., within 0.010 inch of the closed position. However, some flow tubes are relatively hard and stiff as compared to other tubes and it is difficult to squeeze the harder and stiffer tubes, particularly the larger diameter sizes of these tubes, in order to get the cam surfaces engaged to allow turning of the nut. Also, for such tubes, it may be difficult for persons of limited strength to unscrew the nut after pump operation. Further, the cam nut is a relatively expensive item.
In this system, the nut and cam surfaces are located at the outer faces of the clam shells. Because the clam shells are made of plastic and the forces encountered during pump occlusion are high, a gap between the clam shells, increasing in width from front to rear, may occur in some instances. Another complicating factor is that the latch is located at the bottom ends of the clam shells, which are often located closely adjacent a horizontal support table or surface, allowing little room for swinging of a latching mechanism between its latching and unlatching positions. Thus, there is a need for improved means for maintaining the reaction members in closed position to avoid this problem.
There is also a need for improved means for maintaining the compressible flow tube in a predetermined position during a pumping operation. As the rotor rotates, it exerts longitudinal forces on the flow tube in addition to transverse compression forces. The longitudinal forces tend to pull the tube through the pump in the direction of rotation of the rotor. To counter this force, means are provided to grip the tube and prevent it from moving relative to the pump. However, because the tube is compressible, exertion of gripping force may reduce the cross sectional area for flow within the tube, thus increasing resistance to flow and decreasing pump efficiency.
The problem of restraining the tube against longitudinal movement is further complicated by the fact that tubes of various different sizes may be used in a particular pump and that lubricants or other materials may be on the tubes, making them slippery. There is a need for improved means to grip flow tubes of various different sizes without excessively restricting flow therethrough.
The range of tube outer diameters may range, for example, from 0.156 inch to 0.500 inch. Some tube retainers have two or three differently sized pairs of gripping notches for gripping tubes of different sizes, with the larger diameter tubes positioned outboard in outboard notches and the small diameter tubes positioned in inboard notches. In retainers of this type, relatively long portions of the tubes are unsupported between the reaction surfaces and the notches, particularly in the case of the smaller diameter tubes in the inboard notches. The unsupported tube lengths tend to vibrate and this has a deleterious effect on tube life and pump efficiency. Also, it would be preferred to increase the arcuate extent of the reaction surfaces so that a greater length of these tubes is engaged by reaction surfaces.
While it has heretofore been proposed to use a pair of opposed large V-shaped notches, each defining a 120.degree. angle to grip up to five different sizes of tubes, this proposal has not overcome all of the aforementioned difficulties which may be overcome with the present invention.